Modern navigation devices as used, for example, in road vehicles greatly facilitate the finding of the right route to a certain destination or point of interest. Additionally, navigation devices increase driving safety by disburdening the driver from both mental and physical acts while driving, such as from handling and analysing a conventional map.
One important feature of most navigation devices is the graphical display of manoeuvre instructions. The driver resorts to the graphical manoeuvre instructions whenever voice guidance has not been understood or the manoeuvre is too complex to be grasped from mere voice guidance. Complex driving manoeuvres are typically encountered in bigger cities with confusing road junctions and broad roads having many road lanes.
To efficiently assist the driver during junction manoeuvres, current navigation devices display a direct visual rendering of map data for a road portion including the junction (sometimes together with a line or arrow indicative of the required junction manoeuvre). Instead of simply showing a direct visual rendering of the map data, some more sophisticated navigation devices are capable of displaying a pre-rendered image of the actual junction geometry. A manoeuvre graphics visualizing an image of the actual junction geometry is of course more instructive than the mere rendering of the corresponding map data. It has empirically been found that despite this advantage, current navigation devices display the actual junction geometry only for motor-way exits, but not for other junction types that would benefit from enhanced manoeuvre graphics, such as roundabouts. This fact is attributed to the comparatively high memory requirements of re-rendered images. As is well known, memory is still a limited resource in particular in mobile navigation devices.